1. Field of the Invention
The present invention is in the fields of solid state manufacturing, including material joining or welding and additive manufacturing. In particular, the invention is in the field of additive friction-stir joining of materials.
2. Description of Related Art
Friction-stir processing provides for the solid state joining of pieces of metal at a joint region through the generation of frictional heat at the joint and opposed portions of the metal pieces by cyclical movements of a tool piece that is harder than the metal pieces. An example of this is provided by International Application Publication No. PCT/GB1992/002203. Frictional heat produced between the substrate and the tool during the process causes the opposed portions of the substrate to soften, and mechanical intermixing and pressure cause the two materials to join. Typically, two materials are placed side-by-side and are joined together at the seam between the two.
Additive friction stir techniques employ an additive process for joining materials. See, for example, U.S. Pat. Nos. 8,636,194; 8,632,850; 8,875,976; and 8,397,974, the contents of which are hereby incorporated by reference in their entireties. Additive friction stir processes use shear-induced interfacial heating and plastic deformation to deposit metallic coatings onto metal substrates. Coatings prepared using additive friction stir techniques have bond strengths superior to those of thermally sprayed coatings, and have the potential to enhance corrosion resistance, enhance wear resistance, repair damaged or worn surfaces, and act as an interfacial layer for bonding metal matrix composites. In this process, the coating material, such as a metal alloy, is forced through a rotating spindle to the substrate surface. Frictional heating occurs at the filler/substrate interface due to the rotational motion of the filler material, such as a rod, at an angular velocity and the downward force applied. The mechanical shearing that occurs at the interface acts to disperse any oxides or boundary layers, resulting in a metallurgical bond between the substrate and coating. As the substrate moves relative to the tool, the coating is extruded under the rotating shoulder of the stirring tool.
Solid state joining processes that are currently available do not use additional filler material and typically require plunging of a profiled tool into the base metal. The plunging of the tool tends to cause considerable tool wear making it unusable and also introduces contaminates into the weld. This problem becomes more severe with materials having a high melting point such as steel, nickel-based alloys, cobalt-based alloys, titanium-based alloys and refractory metals. In addition, the manufacturing of profiled tools are very challenging, time consuming and costly. Thus, there is a need in the art for new solid state joining processes.